v26.2.1

changelog.md

@@ -1,5 +1,25 @@
 # Changelog
 
+## 2026-03-23 - 26.2.1 - fix(rustproxy-http)
+include the upstream request URL when caching H3 Alt-Svc discoveries
+
+- Tracks the request path that triggered Alt-Svc discovery in connection activity state
+- Adds request URL context to Alt-Svc debug logging and protocol cache insertion reasons for better traceability
+
+## 2026-03-23 - 26.2.0 - feat(protocol-cache)
+add sliding TTL re-probing and eviction for backend protocol detection
+
+- extend protocol cache entries and metrics with last accessed and last probed timestamps
+- trigger periodic ALPN re-probes for cached H1/H2 entries while keeping active entries alive with a sliding 1 day TTL
+- log protocol transitions with reasons and evict cache entries when all protocol fallback attempts fail
+
+## 2026-03-22 - 26.1.0 - feat(rustproxy-http)
+add protocol failure suppression, h3 fallback escalation, and protocol cache metrics exposure
+
+- introduces escalating cooldowns for failed H2/H3 protocol detection to prevent repeated upgrades to unstable backends
+- adds within-request escalation to cached HTTP/3 when TCP or TLS backend connections fail in auto-detect mode
+- exposes detected protocol cache entries and suppression state through Rust metrics and the TypeScript metrics adapter
+
 ## 2026-03-21 - 26.0.0 - BREAKING CHANGE(ts-api,rustproxy)
 remove deprecated TypeScript protocol and utility exports while hardening QUIC, HTTP/3, WebSocket, and rate limiter cleanup paths
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@push.rocks/smartproxy",
-  "version": "26.0.0",
+  "version": "26.2.1",
   "private": false,
   "description": "A powerful proxy package with unified route-based configuration for high traffic management. Features include SSL/TLS support, flexible routing patterns, WebSocket handling, advanced security options, and automatic ACME certificate management.",
   "main": "dist_ts/index.js",

rust/crates/rustproxy-http/src/protocol_cache.rs

@@ -1,43 +1,99 @@
-//! Bounded, TTL-based protocol detection cache for backend protocol auto-detection.
+//! Bounded, sliding-TTL protocol detection cache with periodic re-probing and failure suppression.
 //!
 //! Caches the detected protocol (H1, H2, or H3) per backend endpoint and requested
 //! domain (host:port + requested_host). This prevents cache oscillation when multiple
 //! frontend domains share the same backend but differ in protocol support.
 //!
-//! H3 detection uses the browser model: Alt-Svc headers from H1/H2 responses are
-//! parsed and cached, including the advertised H3 port (which may differ from TCP).
+//! ## Sliding TTL
+//!
+//! Each cache hit refreshes the entry's expiry timer (`last_accessed_at`). Entries
+//! remain valid for up to 1 day of continuous use. Every 5 minutes, the next request
+//! triggers an inline ALPN re-probe to verify the cached protocol is still correct.
+//!
+//! ## Upgrade signals
+//!
+//! - ALPN (TLS handshake) → detects H2 vs H1
+//! - Alt-Svc (response header) → advertises H3
+//!
+//! ## Protocol transitions
+//!
+//! All protocol changes are logged at `info!()` level with the reason:
+//! "Protocol transition: H1 → H2 because periodic ALPN re-probe"
+//!
+//! ## Failure suppression
+//!
+//! When a protocol fails, `record_failure()` prevents upgrade signals from
+//! re-introducing it until an escalating cooldown expires (5s → 10s → ... → 300s).
+//! Within-request escalation is allowed via `can_retry()` after a 5s minimum gap.
+//!
+//! ## Total failure eviction
+//!
+//! When all protocols (H3, H2, H1) fail for a backend, the cache entry is evicted
+//! entirely via `evict()`, forcing a fresh probe on the next request.
+//!
+//! Cascading: when a lower protocol also fails, higher protocol cooldowns are
+//! reduced to 5s remaining (not instant clear), preventing tight retry loops.
 
 use std::sync::Arc;
 use std::time::{Duration, Instant};
 
 use dashmap::DashMap;
-use tracing::debug;
+use tracing::{debug, info};
 
-/// TTL for cached protocol detection results.
-/// After this duration, the next request will re-probe the backend.
-const PROTOCOL_CACHE_TTL: Duration = Duration::from_secs(300); // 5 minutes
+/// Sliding TTL for cached protocol detection results.
+/// Entries that haven't been accessed for this duration are evicted.
+/// Each `get()` call refreshes the timer (sliding window).
+const PROTOCOL_CACHE_TTL: Duration = Duration::from_secs(86400); // 1 day
+
+/// Interval between inline ALPN re-probes for H1/H2 entries.
+/// When a cached entry's `last_probed_at` exceeds this, the next request
+/// triggers an ALPN re-probe to verify the backend still speaks the same protocol.
+const PROTOCOL_REPROBE_INTERVAL: Duration = Duration::from_secs(300); // 5 minutes
 
 /// Maximum number of entries in the protocol cache.
-/// Prevents unbounded growth when backends come and go.
 const PROTOCOL_CACHE_MAX_ENTRIES: usize = 4096;
 
-/// Background cleanup interval for the protocol cache.
+/// Background cleanup interval.
 const PROTOCOL_CACHE_CLEANUP_INTERVAL: Duration = Duration::from_secs(60);
 
+/// Minimum cooldown between retry attempts of a failed protocol.
+const PROTOCOL_FAILURE_COOLDOWN: Duration = Duration::from_secs(5);
+
+/// Maximum cooldown (escalation ceiling).
+const PROTOCOL_FAILURE_MAX_COOLDOWN: Duration = Duration::from_secs(300);
+
+/// Consecutive failure count at which cooldown reaches maximum.
+/// 5s × 2^5 = 160s, 5s × 2^6 = 320s → capped at 300s.
+const PROTOCOL_FAILURE_ESCALATION_CAP: u32 = 6;
+
 /// Detected backend protocol.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum DetectedProtocol {
     H1,
     H2,
     H3,
 }
 
+impl std::fmt::Display for DetectedProtocol {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            DetectedProtocol::H1 => write!(f, "H1"),
+            DetectedProtocol::H2 => write!(f, "H2"),
+            DetectedProtocol::H3 => write!(f, "H3"),
+        }
+    }
+}
+
 /// Result of a protocol cache lookup.
 #[derive(Debug, Clone, Copy)]
 pub struct CachedProtocol {
     pub protocol: DetectedProtocol,
     /// For H3: the port advertised by Alt-Svc (may differ from TCP port).
     pub h3_port: Option<u16>,
+    /// True if the entry's `last_probed_at` exceeds `PROTOCOL_REPROBE_INTERVAL`.
+    /// Caller should perform an inline ALPN re-probe and call `update_probe_result()`.
+    /// Always `false` for H3 entries (H3 is discovered via Alt-Svc, not ALPN).
+    pub needs_reprobe: bool,
 }
 
 /// Key for the protocol cache: (host, port, requested_host).
@@ -50,24 +106,111 @@ pub struct ProtocolCacheKey {
     pub requested_host: Option<String>,
 }
 
-/// A cached protocol detection result with a timestamp.
+/// A cached protocol detection result with timestamps.
 struct CachedEntry {
     protocol: DetectedProtocol,
+    /// When this protocol was first detected (or last changed).
     detected_at: Instant,
+    /// Last time any request used this entry (sliding-window TTL).
+    last_accessed_at: Instant,
+    /// Last time an ALPN re-probe was performed for this entry.
+    last_probed_at: Instant,
     /// For H3: the port advertised by Alt-Svc (may differ from TCP port).
     h3_port: Option<u16>,
 }
 
-/// Bounded, TTL-based protocol detection cache.
+/// Failure record for a single protocol level.
+#[derive(Debug, Clone)]
+struct FailureRecord {
+    /// When the failure was last recorded.
+    failed_at: Instant,
+    /// Current cooldown duration. Escalates on consecutive failures.
+    cooldown: Duration,
+    /// Number of consecutive failures (for escalation).
+    consecutive_failures: u32,
+}
+
+/// Per-key failure state. Tracks failures at each upgradeable protocol level.
+/// H1 is never tracked (it's the protocol floor — nothing to fall back to).
+#[derive(Debug, Clone, Default)]
+struct FailureState {
+    h2: Option<FailureRecord>,
+    h3: Option<FailureRecord>,
+}
+
+impl FailureState {
+    fn is_empty(&self) -> bool {
+        self.h2.is_none() && self.h3.is_none()
+    }
+
+    fn all_expired(&self) -> bool {
+        let h2_expired = self.h2.as_ref()
+            .map(|r| r.failed_at.elapsed() >= r.cooldown)
+            .unwrap_or(true);
+        let h3_expired = self.h3.as_ref()
+            .map(|r| r.failed_at.elapsed() >= r.cooldown)
+            .unwrap_or(true);
+        h2_expired && h3_expired
+    }
+
+    fn get(&self, protocol: DetectedProtocol) -> Option<&FailureRecord> {
+        match protocol {
+            DetectedProtocol::H2 => self.h2.as_ref(),
+            DetectedProtocol::H3 => self.h3.as_ref(),
+            DetectedProtocol::H1 => None,
+        }
+    }
+
+    fn get_mut(&mut self, protocol: DetectedProtocol) -> &mut Option<FailureRecord> {
+        match protocol {
+            DetectedProtocol::H2 => &mut self.h2,
+            DetectedProtocol::H3 => &mut self.h3,
+            DetectedProtocol::H1 => unreachable!("H1 failures are never recorded"),
+        }
+    }
+}
+
+/// Snapshot of a single protocol cache entry, suitable for metrics/UI display.
+#[derive(Debug, Clone)]
+pub struct ProtocolCacheEntry {
+    pub host: String,
+    pub port: u16,
+    pub domain: Option<String>,
+    pub protocol: String,
+    pub h3_port: Option<u16>,
+    pub age_secs: u64,
+    pub last_accessed_secs: u64,
+    pub last_probed_secs: u64,
+    pub h2_suppressed: bool,
+    pub h3_suppressed: bool,
+    pub h2_cooldown_remaining_secs: Option<u64>,
+    pub h3_cooldown_remaining_secs: Option<u64>,
+    pub h2_consecutive_failures: Option<u32>,
+    pub h3_consecutive_failures: Option<u32>,
+}
+
+/// Exponential backoff: PROTOCOL_FAILURE_COOLDOWN × 2^(n-1), capped at MAX.
+fn escalate_cooldown(consecutive: u32) -> Duration {
+    let base = PROTOCOL_FAILURE_COOLDOWN.as_secs();
+    let exp = consecutive.saturating_sub(1).min(63) as u64;
+    let secs = base.saturating_mul(1u64.checked_shl(exp as u32).unwrap_or(u64::MAX));
+    Duration::from_secs(secs.min(PROTOCOL_FAILURE_MAX_COOLDOWN.as_secs()))
+}
+
+/// Bounded, sliding-TTL protocol detection cache with failure suppression.
 ///
 /// Memory safety guarantees:
 /// - Hard cap at `PROTOCOL_CACHE_MAX_ENTRIES` — cannot grow unboundedly.
-/// - TTL expiry — stale entries naturally age out on lookup.
+/// - Sliding TTL expiry — entries age out after 1 day without access.
 /// - Background cleanup task — proactively removes expired entries every 60s.
 /// - `clear()` — called on route updates to discard stale detections.
 /// - `Drop` — aborts the background task to prevent dangling tokio tasks.
 pub struct ProtocolCache {
     cache: Arc<DashMap<ProtocolCacheKey, CachedEntry>>,
+    /// Generic protocol failure suppression map. Tracks per-protocol failure
+    /// records (H2, H3) for each cache key. Used to prevent upgrade signals
+    /// (ALPN, Alt-Svc) from re-introducing failed protocols.
+    failures: Arc<DashMap<ProtocolCacheKey, FailureState>>,
     cleanup_handle: Option<tokio::task::JoinHandle<()>>,
 }
 
@@ -75,26 +218,40 @@ impl ProtocolCache {
     /// Create a new protocol cache and start the background cleanup task.
     pub fn new() -> Self {
         let cache: Arc<DashMap<ProtocolCacheKey, CachedEntry>> = Arc::new(DashMap::new());
+        let failures: Arc<DashMap<ProtocolCacheKey, FailureState>> = Arc::new(DashMap::new());
         let cache_clone = Arc::clone(&cache);
+        let failures_clone = Arc::clone(&failures);
         let cleanup_handle = tokio::spawn(async move {
-            Self::cleanup_loop(cache_clone).await;
+            Self::cleanup_loop(cache_clone, failures_clone).await;
         });
 
         Self {
             cache,
+            failures,
             cleanup_handle: Some(cleanup_handle),
         }
     }
 
     /// Look up the cached protocol for a backend endpoint.
+    ///
     /// Returns `None` if not cached or expired (caller should probe via ALPN).
+    /// On hit, refreshes `last_accessed_at` (sliding TTL) and sets `needs_reprobe`
+    /// if the entry hasn't been probed in over 5 minutes (H1/H2 only).
     pub fn get(&self, key: &ProtocolCacheKey) -> Option<CachedProtocol> {
-        let entry = self.cache.get(key)?;
-        if entry.detected_at.elapsed() < PROTOCOL_CACHE_TTL {
-            debug!("Protocol cache hit: {:?} for {}:{} (requested: {:?})", entry.protocol, key.host, key.port, key.requested_host);
+        let mut entry = self.cache.get_mut(key)?;
+        if entry.last_accessed_at.elapsed() < PROTOCOL_CACHE_TTL {
+            // Refresh sliding TTL
+            entry.last_accessed_at = Instant::now();
+
+            // H3 is the ceiling — can't ALPN-probe for H3 (discovered via Alt-Svc).
+            // Only H1/H2 entries trigger periodic re-probing.
+            let needs_reprobe = entry.protocol != DetectedProtocol::H3
+                && entry.last_probed_at.elapsed() >= PROTOCOL_REPROBE_INTERVAL;
+
             Some(CachedProtocol {
                 protocol: entry.protocol,
                 h3_port: entry.h3_port,
+                needs_reprobe,
             })
         } else {
             // Expired — remove and return None to trigger re-probe
@@ -105,47 +262,328 @@ impl ProtocolCache {
     }
 
     /// Insert a detected protocol into the cache.
-    /// If the cache is at capacity, evict the oldest entry first.
-    pub fn insert(&self, key: ProtocolCacheKey, protocol: DetectedProtocol) {
-        self.insert_with_h3_port(key, protocol, None);
+    /// Returns `false` if suppressed due to active failure suppression.
+    ///
+    /// **Key semantic**: only suppresses if the protocol being inserted matches
+    /// a suppressed protocol. H1 inserts are NEVER suppressed — downgrades
+    /// always succeed.
+    pub fn insert(&self, key: ProtocolCacheKey, protocol: DetectedProtocol, reason: &str) -> bool {
+        if self.is_suppressed(&key, protocol) {
+            debug!(
+                host = %key.host, port = %key.port, domain = ?key.requested_host,
+                protocol = ?protocol,
+                "Protocol cache insert suppressed — recent failure"
+            );
+            return false;
+        }
+        self.insert_internal(key, protocol, None, reason);
+        true
     }
 
     /// Insert an H3 detection result with the Alt-Svc advertised port.
-    pub fn insert_h3(&self, key: ProtocolCacheKey, h3_port: u16) {
-        self.insert_with_h3_port(key, DetectedProtocol::H3, Some(h3_port));
+    /// Returns `false` if H3 is suppressed.
+    pub fn insert_h3(&self, key: ProtocolCacheKey, h3_port: u16, reason: &str) -> bool {
+        if self.is_suppressed(&key, DetectedProtocol::H3) {
+            debug!(
+                host = %key.host, port = %key.port, domain = ?key.requested_host,
+                "H3 upgrade suppressed — recent failure"
+            );
+            return false;
+        }
+        self.insert_internal(key, DetectedProtocol::H3, Some(h3_port), reason);
+        true
     }
 
-    /// Insert a protocol detection result with an optional H3 port.
-    fn insert_with_h3_port(&self, key: ProtocolCacheKey, protocol: DetectedProtocol, h3_port: Option<u16>) {
-        if self.cache.len() >= PROTOCOL_CACHE_MAX_ENTRIES && !self.cache.contains_key(&key) {
-            // Evict the oldest entry to stay within bounds
-            let oldest = self.cache.iter()
-                .min_by_key(|entry| entry.value().detected_at)
-                .map(|entry| entry.key().clone());
-            if let Some(oldest_key) = oldest {
-                self.cache.remove(&oldest_key);
+    /// Update the cache after an inline ALPN re-probe completes.
+    ///
+    /// Always updates `last_probed_at`. If the protocol changed, logs the transition
+    /// and updates the entry. Returns `Some(new_protocol)` if changed, `None` if unchanged.
+    pub fn update_probe_result(
+        &self,
+        key: &ProtocolCacheKey,
+        probed_protocol: DetectedProtocol,
+        reason: &str,
+    ) -> Option<DetectedProtocol> {
+        if let Some(mut entry) = self.cache.get_mut(key) {
+            let old_protocol = entry.protocol;
+            entry.last_probed_at = Instant::now();
+            entry.last_accessed_at = Instant::now();
+
+            if old_protocol != probed_protocol {
+                info!(
+                    host = %key.host, port = %key.port, domain = ?key.requested_host,
+                    old = %old_protocol, new = %probed_protocol, reason = %reason,
+                    "Protocol transition"
+                );
+                entry.protocol = probed_protocol;
+                entry.detected_at = Instant::now();
+                // Clear h3_port if downgrading from H3
+                if old_protocol == DetectedProtocol::H3 && probed_protocol != DetectedProtocol::H3 {
+                    entry.h3_port = None;
+                }
+                return Some(probed_protocol);
+            }
+
+            debug!(
+                host = %key.host, port = %key.port, domain = ?key.requested_host,
+                protocol = %old_protocol, reason = %reason,
+                "Re-probe confirmed — no protocol change"
+            );
+            None
+        } else {
+            // Entry was evicted between the get() and the probe completing.
+            // Insert as a fresh entry.
+            self.insert_internal(key.clone(), probed_protocol, None, reason);
+            Some(probed_protocol)
+        }
+    }
+
+    /// Record a protocol failure. Future `insert()` calls for this protocol
+    /// will be suppressed until the escalating cooldown expires.
+    ///
+    /// Cooldown escalation: 5s → 10s → 20s → 40s → 80s → 160s → 300s.
+    /// Consecutive counter resets if the previous failure is older than 2× its cooldown.
+    ///
+    /// Cascading: when H2 fails, H3 cooldown is reduced to 5s remaining.
+    /// H1 failures are ignored (H1 is the protocol floor).
+    pub fn record_failure(&self, key: ProtocolCacheKey, protocol: DetectedProtocol) {
+        if protocol == DetectedProtocol::H1 {
+            return; // H1 is the floor — nothing to suppress
+        }
+
+        let mut entry = self.failures.entry(key.clone()).or_default();
+
+        let record = entry.get_mut(protocol);
+        let (consecutive, new_cooldown) = match record {
+            Some(existing) if existing.failed_at.elapsed() < existing.cooldown.saturating_mul(2) => {
+                // Still within the "recent" window — escalate
+                let c = existing.consecutive_failures.saturating_add(1)
+                    .min(PROTOCOL_FAILURE_ESCALATION_CAP);
+                (c, escalate_cooldown(c))
+            }
+            _ => {
+                // First failure or old failure that expired long ago — reset
+                (1, PROTOCOL_FAILURE_COOLDOWN)
+            }
+        };
+
+        *record = Some(FailureRecord {
+            failed_at: Instant::now(),
+            cooldown: new_cooldown,
+            consecutive_failures: consecutive,
+        });
+
+        // Cascading: when H2 fails, reduce H3 cooldown to 5s remaining
+        if protocol == DetectedProtocol::H2 {
+            Self::reduce_cooldown_to(entry.h3.as_mut(), PROTOCOL_FAILURE_COOLDOWN);
+        }
+
+        info!(
+            host = %key.host, port = %key.port, domain = ?key.requested_host,
+            protocol = ?protocol,
+            consecutive = consecutive,
+            cooldown_secs = new_cooldown.as_secs(),
+            "Protocol failure recorded — suppressing for {:?}", new_cooldown
+        );
+    }
+
+    /// Check whether a protocol is currently suppressed for the given key.
+    /// Returns `true` if the protocol failed within its cooldown period.
+    /// H1 is never suppressed.
+    pub fn is_suppressed(&self, key: &ProtocolCacheKey, protocol: DetectedProtocol) -> bool {
+        if protocol == DetectedProtocol::H1 {
+            return false;
+        }
+        self.failures.get(key)
+            .and_then(|entry| entry.get(protocol).map(|r| r.failed_at.elapsed() < r.cooldown))
+            .unwrap_or(false)
+    }
+
+    /// Check whether a protocol can be retried (for within-request escalation).
+    /// Returns `true` if there's no failure record OR if ≥5s have passed since
+    /// the last attempt. More permissive than `is_suppressed`.
+    pub fn can_retry(&self, key: &ProtocolCacheKey, protocol: DetectedProtocol) -> bool {
+        if protocol == DetectedProtocol::H1 {
+            return true;
+        }
+        match self.failures.get(key) {
+            Some(entry) => match entry.get(protocol) {
+                Some(r) => r.failed_at.elapsed() >= PROTOCOL_FAILURE_COOLDOWN,
+                None => true, // no failure record
+            },
+            None => true,
+        }
+    }
+
+    /// Record a retry attempt WITHOUT escalating the cooldown.
+    /// Resets the `failed_at` timestamp to prevent rapid retries (5s gate).
+    /// Called before an escalation attempt. If the attempt fails,
+    /// `record_failure` should be called afterward with proper escalation.
+    pub fn record_retry_attempt(&self, key: &ProtocolCacheKey, protocol: DetectedProtocol) {
+        if protocol == DetectedProtocol::H1 {
+            return;
+        }
+        if let Some(mut entry) = self.failures.get_mut(key) {
+            if let Some(ref mut r) = entry.get_mut(protocol) {
+                r.failed_at = Instant::now();
             }
         }
-        self.cache.insert(key, CachedEntry {
-            protocol,
-            detected_at: Instant::now(),
-            h3_port,
-        });
+    }
+
+    /// Clear the failure record for a protocol (it recovered).
+    /// Called when an escalation retry succeeds.
+    pub fn clear_failure(&self, key: &ProtocolCacheKey, protocol: DetectedProtocol) {
+        if protocol == DetectedProtocol::H1 {
+            return;
+        }
+        if let Some(mut entry) = self.failures.get_mut(key) {
+            *entry.get_mut(protocol) = None;
+            if entry.is_empty() {
+                drop(entry);
+                self.failures.remove(key);
+            }
+        }
+    }
+
+    /// Evict a cache entry entirely. Called when all protocol probes (H3, H2, H1)
+    /// have failed for a backend.
+    pub fn evict(&self, key: &ProtocolCacheKey) {
+        self.cache.remove(key);
+        self.failures.remove(key);
+        info!(
+            host = %key.host, port = %key.port, domain = ?key.requested_host,
+            "Cache entry evicted — all protocols failed"
+        );
     }
 
     /// Clear all entries. Called on route updates to discard stale detections.
     pub fn clear(&self) {
         self.cache.clear();
+        self.failures.clear();
     }
 
-    /// Background cleanup loop — removes expired entries every `PROTOCOL_CACHE_CLEANUP_INTERVAL`.
-    async fn cleanup_loop(cache: Arc<DashMap<ProtocolCacheKey, CachedEntry>>) {
+    /// Snapshot all non-expired cache entries for metrics/UI display.
+    pub fn snapshot(&self) -> Vec<ProtocolCacheEntry> {
+        self.cache.iter()
+            .filter(|entry| entry.value().last_accessed_at.elapsed() < PROTOCOL_CACHE_TTL)
+            .map(|entry| {
+                let key = entry.key();
+                let val = entry.value();
+                let failure_info = self.failures.get(key);
+
+                let (h2_sup, h2_cd, h2_cons) = Self::suppression_info(
+                    failure_info.as_deref().and_then(|f| f.h2.as_ref()),
+                );
+                let (h3_sup, h3_cd, h3_cons) = Self::suppression_info(
+                    failure_info.as_deref().and_then(|f| f.h3.as_ref()),
+                );
+
+                ProtocolCacheEntry {
+                    host: key.host.clone(),
+                    port: key.port,
+                    domain: key.requested_host.clone(),
+                    protocol: match val.protocol {
+                        DetectedProtocol::H1 => "h1".to_string(),
+                        DetectedProtocol::H2 => "h2".to_string(),
+                        DetectedProtocol::H3 => "h3".to_string(),
+                    },
+                    h3_port: val.h3_port,
+                    age_secs: val.detected_at.elapsed().as_secs(),
+                    last_accessed_secs: val.last_accessed_at.elapsed().as_secs(),
+                    last_probed_secs: val.last_probed_at.elapsed().as_secs(),
+                    h2_suppressed: h2_sup,
+                    h3_suppressed: h3_sup,
+                    h2_cooldown_remaining_secs: h2_cd,
+                    h3_cooldown_remaining_secs: h3_cd,
+                    h2_consecutive_failures: h2_cons,
+                    h3_consecutive_failures: h3_cons,
+                }
+            })
+            .collect()
+    }
+
+    // --- Internal helpers ---
+
+    /// Insert a protocol detection result with an optional H3 port.
+    /// Logs protocol transitions when overwriting an existing entry.
+    /// No suppression check — callers must check before calling.
+    fn insert_internal(&self, key: ProtocolCacheKey, protocol: DetectedProtocol, h3_port: Option<u16>, reason: &str) {
+        // Check for existing entry to log protocol transitions
+        if let Some(existing) = self.cache.get(&key) {
+            if existing.protocol != protocol {
+                info!(
+                    host = %key.host, port = %key.port, domain = ?key.requested_host,
+                    old = %existing.protocol, new = %protocol, reason = %reason,
+                    "Protocol transition"
+                );
+            }
+            drop(existing);
+        }
+
+        // Evict oldest entry if at capacity
+        if self.cache.len() >= PROTOCOL_CACHE_MAX_ENTRIES && !self.cache.contains_key(&key) {
+            let oldest = self.cache.iter()
+                .min_by_key(|entry| entry.value().last_accessed_at)
+                .map(|entry| entry.key().clone());
+            if let Some(oldest_key) = oldest {
+                self.cache.remove(&oldest_key);
+            }
+        }
+
+        let now = Instant::now();
+        self.cache.insert(key, CachedEntry {
+            protocol,
+            detected_at: now,
+            last_accessed_at: now,
+            last_probed_at: now,
+            h3_port,
+        });
+    }
+
+    /// Reduce a failure record's remaining cooldown to `target`, if it currently
+    /// has MORE than `target` remaining. Never increases cooldown.
+    fn reduce_cooldown_to(record: Option<&mut FailureRecord>, target: Duration) {
+        if let Some(r) = record {
+            let elapsed = r.failed_at.elapsed();
+            if elapsed < r.cooldown {
+                let remaining = r.cooldown - elapsed;
+                if remaining > target {
+                    // Shrink cooldown so it expires in `target` from now
+                    r.cooldown = elapsed + target;
+                }
+            }
+        }
+    }
+
+    /// Extract suppression info from a failure record for metrics.
+    fn suppression_info(record: Option<&FailureRecord>) -> (bool, Option<u64>, Option<u32>) {
+        match record {
+            Some(r) => {
+                let elapsed = r.failed_at.elapsed();
+                let suppressed = elapsed < r.cooldown;
+                let remaining = if suppressed {
+                    Some((r.cooldown - elapsed).as_secs())
+                } else {
+                    None
+                };
+                (suppressed, remaining, Some(r.consecutive_failures))
+            }
+            None => (false, None, None),
+        }
+    }
+
+    /// Background cleanup loop.
+    async fn cleanup_loop(
+        cache: Arc<DashMap<ProtocolCacheKey, CachedEntry>>,
+        failures: Arc<DashMap<ProtocolCacheKey, FailureState>>,
+    ) {
         let mut interval = tokio::time::interval(PROTOCOL_CACHE_CLEANUP_INTERVAL);
         loop {
             interval.tick().await;
 
+            // Clean expired cache entries (sliding TTL based on last_accessed_at)
             let expired: Vec<ProtocolCacheKey> = cache.iter()
-                .filter(|entry| entry.value().detected_at.elapsed() >= PROTOCOL_CACHE_TTL)
+                .filter(|entry| entry.value().last_accessed_at.elapsed() >= PROTOCOL_CACHE_TTL)
                 .map(|entry| entry.key().clone())
                 .collect();
 
@@ -155,6 +593,31 @@ impl ProtocolCache {
                     cache.remove(&key);
                 }
             }
+
+            // Clean fully-expired failure entries
+            let expired_failures: Vec<ProtocolCacheKey> = failures.iter()
+                .filter(|entry| entry.value().all_expired())
+                .map(|entry| entry.key().clone())
+                .collect();
+
+            if !expired_failures.is_empty() {
+                debug!("Protocol cache cleanup: removing {} expired failure entries", expired_failures.len());
+                for key in expired_failures {
+                    failures.remove(&key);
+                }
+            }
+
+            // Safety net: cap failures map at 2× max entries
+            if failures.len() > PROTOCOL_CACHE_MAX_ENTRIES * 2 {
+                let oldest: Vec<ProtocolCacheKey> = failures.iter()
+                    .filter(|e| e.value().all_expired())
+                    .map(|e| e.key().clone())
+                    .take(failures.len() - PROTOCOL_CACHE_MAX_ENTRIES)
+                    .collect();
+                for key in oldest {
+                    failures.remove(&key);
+                }
+            }
         }
     }
 }

rust/crates/rustproxy-http/src/proxy_service.rs

@@ -47,6 +47,8 @@ pub struct ConnActivity {
     /// checks the backend's original response headers for Alt-Svc before our
     /// ResponseFilter injects its own. None when not in auto-detect mode or after H3 failure.
     alt_svc_cache_key: Option<crate::protocol_cache::ProtocolCacheKey>,
+    /// The upstream request path that triggered Alt-Svc discovery. Logged for traceability.
+    alt_svc_request_url: Option<String>,
 }
 
 impl ConnActivity {
@@ -58,6 +60,7 @@ impl ConnActivity {
             start: std::time::Instant::now(),
             active_requests: None,
             alt_svc_cache_key: None,
+            alt_svc_request_url: None,
         }
     }
 }
@@ -311,6 +314,11 @@ impl HttpProxyService {
         self.protocol_cache.clear();
     }
 
+    /// Snapshot the protocol cache for metrics/UI display.
+    pub fn protocol_cache_snapshot(&self) -> Vec<crate::protocol_cache::ProtocolCacheEntry> {
+        self.protocol_cache.snapshot()
+    }
+
     /// Handle an incoming HTTP connection on a plain TCP stream.
     pub async fn handle_connection(
         self: Arc<Self>,
@@ -366,7 +374,7 @@ impl HttpProxyService {
             let cn = cancel_inner.clone();
             let la = Arc::clone(&la_inner);
             let st = start;
-            let ca = ConnActivity { last_activity: Arc::clone(&la_inner), start, active_requests: Some(Arc::clone(&ar_inner)), alt_svc_cache_key: None };
+            let ca = ConnActivity { last_activity: Arc::clone(&la_inner), start, active_requests: Some(Arc::clone(&ar_inner)), alt_svc_cache_key: None, alt_svc_request_url: None };
             async move {
                 let req = req.map(|body| BoxBody::new(body));
                 let result = svc.handle_request(req, peer, port, cn, ca).await;
@@ -701,6 +709,14 @@ impl HttpProxyService {
             port: upstream.port,
             requested_host: host.clone(),
         };
+        // Save cached H3 port for within-request escalation (may be needed later
+        // if TCP connect fails and we escalate to H3 as a last resort)
+        let cached_h3_port = self.protocol_cache.get(&protocol_cache_key)
+            .and_then(|c| c.h3_port);
+
+        // Track whether this ALPN probe is a periodic re-probe (vs first-time detection)
+        let mut is_reprobe = false;
+
         let protocol_decision = match backend_protocol_mode {
             rustproxy_config::BackendProtocol::Http1 => ProtocolDecision::H1,
             rustproxy_config::BackendProtocol::Http2 => ProtocolDecision::H2,
@@ -711,19 +727,40 @@ impl HttpProxyService {
                     ProtocolDecision::H1
                 } else {
                     match self.protocol_cache.get(&protocol_cache_key) {
+                        Some(cached) if cached.needs_reprobe => {
+                            // Entry exists but 5+ minutes since last probe — force ALPN re-probe
+                            // (only fires for H1/H2; H3 entries have needs_reprobe=false)
+                            is_reprobe = true;
+                            ProtocolDecision::AlpnProbe
+                        }
                         Some(cached) => match cached.protocol {
                             crate::protocol_cache::DetectedProtocol::H3 => {
-                                if let Some(h3_port) = cached.h3_port {
+                                if self.protocol_cache.is_suppressed(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3) {
+                                    // H3 cached but suppressed — fall back to ALPN probe
+                                    ProtocolDecision::AlpnProbe
+                                } else if let Some(h3_port) = cached.h3_port {
                                     ProtocolDecision::H3 { port: h3_port }
                                 } else {
-                                    // H3 cached but no port — fall back to ALPN probe
                                     ProtocolDecision::AlpnProbe
                                 }
                             }
-                            crate::protocol_cache::DetectedProtocol::H2 => ProtocolDecision::H2,
+                            crate::protocol_cache::DetectedProtocol::H2 => {
+                                if self.protocol_cache.is_suppressed(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H2) {
+                                    ProtocolDecision::H1
+                                } else {
+                                    ProtocolDecision::H2
+                                }
+                            }
                             crate::protocol_cache::DetectedProtocol::H1 => ProtocolDecision::H1,
                         },
-                        None => ProtocolDecision::AlpnProbe,
+                        None => {
+                            // Cache miss — skip ALPN probe if H2 is suppressed
+                            if self.protocol_cache.is_suppressed(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H2) {
+                                ProtocolDecision::H1
+                            } else {
+                                ProtocolDecision::AlpnProbe
+                            }
+                        }
                     }
                 }
             }
@@ -741,6 +778,7 @@ impl HttpProxyService {
         // the backend's original Alt-Svc header before ResponseFilter injects our own.
         if is_auto_detect_mode {
             conn_activity.alt_svc_cache_key = Some(protocol_cache_key.clone());
+            conn_activity.alt_svc_request_url = Some(upstream_path.to_string());
         }
 
         // --- H3 path: try QUIC connection before TCP ---
@@ -776,8 +814,16 @@ impl HttpProxyService {
                     return result;
                 }
                 Err(e) => {
-                    warn!(backend = %upstream_key, error = %e,
+                    warn!(backend = %upstream_key, domain = %domain_str, error = %e,
                         "H3 backend connect failed, falling back to H2/H1");
+                    // Record failure with escalating cooldown — prevents Alt-Svc
+                    // from re-upgrading to H3 during cooldown period
+                    if is_auto_detect_mode {
+                        self.protocol_cache.record_failure(
+                            protocol_cache_key.clone(),
+                            crate::protocol_cache::DetectedProtocol::H3,
+                        );
+                    }
                     // Suppress Alt-Svc caching for the fallback to prevent re-caching H3
                     // from our own injected Alt-Svc header or a stale backend Alt-Svc
                     conn_activity.alt_svc_cache_key = None;
@@ -860,7 +906,7 @@ impl HttpProxyService {
                         let alpn = tls.get_ref().1.alpn_protocol();
                         let is_h2 = alpn.map(|p| p == b"h2").unwrap_or(false);
 
-                        // Cache the result
+                        // Cache the result (or update existing entry for re-probes)
                         let cache_key = crate::protocol_cache::ProtocolCacheKey {
                             host: upstream.host.clone(),
                             port: upstream.port,
@@ -871,13 +917,18 @@ impl HttpProxyService {
                         } else {
                             crate::protocol_cache::DetectedProtocol::H1
                         };
-                        self.protocol_cache.insert(cache_key, detected);
+                        if is_reprobe {
+                            self.protocol_cache.update_probe_result(&cache_key, detected, "periodic ALPN re-probe");
+                        } else {
+                            self.protocol_cache.insert(cache_key, detected, "initial ALPN detection");
+                        }
 
                         info!(
                             backend = %upstream_key,
                             domain = %domain_str,
                             protocol = if is_h2 { "h2" } else { "h1" },
                             connect_time_ms = %connect_start.elapsed().as_millis(),
+                            reprobe = is_reprobe,
                             "Backend protocol detected via ALPN"
                         );
 
@@ -899,6 +950,38 @@ impl HttpProxyService {
                     );
                     self.metrics.backend_connect_error(&upstream_key);
                     self.upstream_selector.connection_ended(&upstream_key);
+
+                    // --- Within-request escalation: try H3 via QUIC if retryable ---
+                    if is_auto_detect_mode {
+                        if let Some(h3_port) = cached_h3_port {
+                            if self.protocol_cache.can_retry(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3) {
+                                self.protocol_cache.record_retry_attempt(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                debug!(backend = %upstream_key, domain = %domain_str, "TLS connect failed — escalating to H3");
+                                match self.connect_quic_backend(&upstream.host, h3_port).await {
+                                    Ok(quic_conn) => {
+                                        self.protocol_cache.clear_failure(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                        self.protocol_cache.insert_h3(protocol_cache_key.clone(), h3_port, "recovery — TLS failed, H3 succeeded");
+                                        let h3_pool_key = crate::connection_pool::PoolKey {
+                                            host: upstream.host.clone(), port: h3_port, use_tls: true,
+                                            protocol: crate::connection_pool::PoolProtocol::H3,
+                                        };
+                                        let result = self.forward_h3(
+                                            quic_conn, parts, body, upstream_headers, &upstream_path,
+                                            route_match.route, route_id, &ip_str, &h3_pool_key, domain_str, &conn_activity, &upstream_key,
+                                        ).await;
+                                        self.upstream_selector.connection_ended(&upstream_key);
+                                        return result;
+                                    }
+                                    Err(e3) => {
+                                        debug!(backend = %upstream_key, error = %e3, "H3 escalation also failed");
+                                        self.protocol_cache.record_failure(protocol_cache_key.clone(), crate::protocol_cache::DetectedProtocol::H3);
+                                    }
+                                }
+                            }
+                        }
+                        // All protocols failed — evict cache entry
+                        self.protocol_cache.evict(&protocol_cache_key);
+                    }
                     return Ok(error_response(StatusCode::BAD_GATEWAY, "Backend TLS unavailable"));
                 }
                 Err(_) => {
@@ -910,6 +993,38 @@ impl HttpProxyService {
                     );
                     self.metrics.backend_connect_error(&upstream_key);
                     self.upstream_selector.connection_ended(&upstream_key);
+
+                    // --- Within-request escalation: try H3 via QUIC if retryable ---
+                    if is_auto_detect_mode {
+                        if let Some(h3_port) = cached_h3_port {
+                            if self.protocol_cache.can_retry(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3) {
+                                self.protocol_cache.record_retry_attempt(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                debug!(backend = %upstream_key, domain = %domain_str, "TLS connect timeout — escalating to H3");
+                                match self.connect_quic_backend(&upstream.host, h3_port).await {
+                                    Ok(quic_conn) => {
+                                        self.protocol_cache.clear_failure(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                        self.protocol_cache.insert_h3(protocol_cache_key.clone(), h3_port, "recovery — TLS timeout, H3 succeeded");
+                                        let h3_pool_key = crate::connection_pool::PoolKey {
+                                            host: upstream.host.clone(), port: h3_port, use_tls: true,
+                                            protocol: crate::connection_pool::PoolProtocol::H3,
+                                        };
+                                        let result = self.forward_h3(
+                                            quic_conn, parts, body, upstream_headers, &upstream_path,
+                                            route_match.route, route_id, &ip_str, &h3_pool_key, domain_str, &conn_activity, &upstream_key,
+                                        ).await;
+                                        self.upstream_selector.connection_ended(&upstream_key);
+                                        return result;
+                                    }
+                                    Err(e3) => {
+                                        debug!(backend = %upstream_key, error = %e3, "H3 escalation also failed");
+                                        self.protocol_cache.record_failure(protocol_cache_key.clone(), crate::protocol_cache::DetectedProtocol::H3);
+                                    }
+                                }
+                            }
+                        }
+                        // All protocols failed — evict cache entry
+                        self.protocol_cache.evict(&protocol_cache_key);
+                    }
                     return Ok(error_response(StatusCode::GATEWAY_TIMEOUT, "Backend TLS connect timeout"));
                 }
             }
@@ -937,6 +1052,38 @@ impl HttpProxyService {
                     );
                     self.metrics.backend_connect_error(&upstream_key);
                     self.upstream_selector.connection_ended(&upstream_key);
+
+                    // --- Within-request escalation: try H3 via QUIC if retryable ---
+                    if is_auto_detect_mode {
+                        if let Some(h3_port) = cached_h3_port {
+                            if self.protocol_cache.can_retry(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3) {
+                                self.protocol_cache.record_retry_attempt(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                debug!(backend = %upstream_key, domain = %domain_str, "TCP connect failed — escalating to H3");
+                                match self.connect_quic_backend(&upstream.host, h3_port).await {
+                                    Ok(quic_conn) => {
+                                        self.protocol_cache.clear_failure(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                        self.protocol_cache.insert_h3(protocol_cache_key.clone(), h3_port, "recovery — TCP failed, H3 succeeded");
+                                        let h3_pool_key = crate::connection_pool::PoolKey {
+                                            host: upstream.host.clone(), port: h3_port, use_tls: true,
+                                            protocol: crate::connection_pool::PoolProtocol::H3,
+                                        };
+                                        let result = self.forward_h3(
+                                            quic_conn, parts, body, upstream_headers, &upstream_path,
+                                            route_match.route, route_id, &ip_str, &h3_pool_key, domain_str, &conn_activity, &upstream_key,
+                                        ).await;
+                                        self.upstream_selector.connection_ended(&upstream_key);
+                                        return result;
+                                    }
+                                    Err(e3) => {
+                                        debug!(backend = %upstream_key, error = %e3, "H3 escalation also failed");
+                                        self.protocol_cache.record_failure(protocol_cache_key.clone(), crate::protocol_cache::DetectedProtocol::H3);
+                                    }
+                                }
+                            }
+                        }
+                        // All protocols failed — evict cache entry
+                        self.protocol_cache.evict(&protocol_cache_key);
+                    }
                     return Ok(error_response(StatusCode::BAD_GATEWAY, "Backend unavailable"));
                 }
                 Err(_) => {
@@ -948,6 +1095,38 @@ impl HttpProxyService {
                     );
                     self.metrics.backend_connect_error(&upstream_key);
                     self.upstream_selector.connection_ended(&upstream_key);
+
+                    // --- Within-request escalation: try H3 via QUIC if retryable ---
+                    if is_auto_detect_mode {
+                        if let Some(h3_port) = cached_h3_port {
+                            if self.protocol_cache.can_retry(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3) {
+                                self.protocol_cache.record_retry_attempt(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                debug!(backend = %upstream_key, domain = %domain_str, "TCP connect timeout — escalating to H3");
+                                match self.connect_quic_backend(&upstream.host, h3_port).await {
+                                    Ok(quic_conn) => {
+                                        self.protocol_cache.clear_failure(&protocol_cache_key, crate::protocol_cache::DetectedProtocol::H3);
+                                        self.protocol_cache.insert_h3(protocol_cache_key.clone(), h3_port, "recovery — TCP timeout, H3 succeeded");
+                                        let h3_pool_key = crate::connection_pool::PoolKey {
+                                            host: upstream.host.clone(), port: h3_port, use_tls: true,
+                                            protocol: crate::connection_pool::PoolProtocol::H3,
+                                        };
+                                        let result = self.forward_h3(
+                                            quic_conn, parts, body, upstream_headers, &upstream_path,
+                                            route_match.route, route_id, &ip_str, &h3_pool_key, domain_str, &conn_activity, &upstream_key,
+                                        ).await;
+                                        self.upstream_selector.connection_ended(&upstream_key);
+                                        return result;
+                                    }
+                                    Err(e3) => {
+                                        debug!(backend = %upstream_key, error = %e3, "H3 escalation also failed");
+                                        self.protocol_cache.record_failure(protocol_cache_key.clone(), crate::protocol_cache::DetectedProtocol::H3);
+                                    }
+                                }
+                            }
+                        }
+                        // All protocols failed — evict cache entry
+                        self.protocol_cache.evict(&protocol_cache_key);
+                    }
                     return Ok(error_response(StatusCode::GATEWAY_TIMEOUT, "Backend connect timeout"));
                 }
             }
@@ -1416,7 +1595,12 @@ impl HttpProxyService {
                     port: upstream.port,
                     requested_host: requested_host.clone(),
                 };
-                self.protocol_cache.insert(cache_key, crate::protocol_cache::DetectedProtocol::H1);
+                // Record H2 failure (escalating cooldown) before downgrading cache to H1
+                self.protocol_cache.record_failure(
+                    cache_key.clone(),
+                    crate::protocol_cache::DetectedProtocol::H2,
+                );
+                self.protocol_cache.insert(cache_key.clone(), crate::protocol_cache::DetectedProtocol::H1, "H2 handshake timeout — downgrade");
 
                 match self.reconnect_backend(upstream, domain, backend_key).await {
                     Some(fallback_backend) => {
@@ -1435,6 +1619,8 @@ impl HttpProxyService {
                         result
                     }
                     None => {
+                        // H2 failed and H1 reconnect also failed — evict cache
+                        self.protocol_cache.evict(&cache_key);
                         Ok(error_response(StatusCode::BAD_GATEWAY, "Backend unavailable after H2 timeout fallback"))
                     }
                 }
@@ -1549,13 +1735,17 @@ impl HttpProxyService {
                 self.metrics.backend_h2_failure(backend_key);
                 self.metrics.backend_handshake_error(backend_key);
 
-                // Update cache to H1 so subsequent requests skip H2
+                // Record H2 failure (escalating cooldown) and downgrade cache to H1
                 let cache_key = crate::protocol_cache::ProtocolCacheKey {
                     host: upstream.host.clone(),
                     port: upstream.port,
                     requested_host: requested_host.clone(),
                 };
-                self.protocol_cache.insert(cache_key, crate::protocol_cache::DetectedProtocol::H1);
+                self.protocol_cache.record_failure(
+                    cache_key.clone(),
+                    crate::protocol_cache::DetectedProtocol::H2,
+                );
+                self.protocol_cache.insert(cache_key.clone(), crate::protocol_cache::DetectedProtocol::H1, "H2 handshake error — downgrade");
 
                 // Reconnect for H1 (the original io was consumed by the failed h2 handshake)
                 match self.reconnect_backend(upstream, domain, backend_key).await {
@@ -1576,6 +1766,8 @@ impl HttpProxyService {
                         result
                     }
                     None => {
+                        // H2 failed and H1 reconnect also failed — evict cache
+                        self.protocol_cache.evict(&cache_key);
                         Ok(error_response(StatusCode::BAD_GATEWAY, "Backend unavailable after H2 fallback"))
                     }
                 }
@@ -1791,8 +1983,10 @@ impl HttpProxyService {
         if let Some(ref cache_key) = conn_activity.alt_svc_cache_key {
             if let Some(alt_svc) = resp_parts.headers.get("alt-svc").and_then(|v| v.to_str().ok()) {
                 if let Some(h3_port) = parse_alt_svc_h3_port(alt_svc) {
-                    debug!(h3_port, "Backend advertises H3 via Alt-Svc");
-                    self.protocol_cache.insert_h3(cache_key.clone(), h3_port);
+                    let url = conn_activity.alt_svc_request_url.as_deref().unwrap_or("-");
+                    debug!(h3_port, url, "Backend advertises H3 via Alt-Svc");
+                    let reason = format!("Alt-Svc response header ({})", url);
+                    self.protocol_cache.insert_h3(cache_key.clone(), h3_port, &reason);
                 }
             }
         }
@@ -2569,7 +2763,7 @@ impl HttpProxyService {
         let connecting = self.quinn_client_endpoint.connect(addr, &server_name)?;
 
         let connection = tokio::time::timeout(QUIC_CONNECT_TIMEOUT, connecting).await
-            .map_err(|_| "QUIC connect timeout (3s)")??;
+            .map_err(|_| format!("QUIC connect timeout (3s) for {}", host))??;
 
         debug!("QUIC backend connection established to {}:{}", host, port);
         Ok(connection)

rust/crates/rustproxy-metrics/src/collector.rs

@@ -31,6 +31,8 @@ pub struct Metrics {
     pub total_udp_sessions: u64,
     pub total_datagrams_in: u64,
     pub total_datagrams_out: u64,
+    // Protocol detection cache snapshot (populated by RustProxy from HttpProxyService)
+    pub detected_protocols: Vec<ProtocolCacheEntryMetric>,
 }
 
 /// Per-route metrics.
@@ -76,6 +78,27 @@ pub struct BackendMetrics {
     pub h2_failures: u64,
 }
 
+/// Protocol cache entry for metrics/UI display.
+/// Populated from the HTTP proxy service's protocol detection cache.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ProtocolCacheEntryMetric {
+    pub host: String,
+    pub port: u16,
+    pub domain: Option<String>,
+    pub protocol: String,
+    pub h3_port: Option<u16>,
+    pub age_secs: u64,
+    pub last_accessed_secs: u64,
+    pub last_probed_secs: u64,
+    pub h2_suppressed: bool,
+    pub h3_suppressed: bool,
+    pub h2_cooldown_remaining_secs: Option<u64>,
+    pub h3_cooldown_remaining_secs: Option<u64>,
+    pub h2_consecutive_failures: Option<u32>,
+    pub h3_consecutive_failures: Option<u32>,
+}
+
 /// Statistics snapshot.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
@@ -824,6 +847,7 @@ impl MetricsCollector {
             total_udp_sessions: self.total_udp_sessions.load(Ordering::Relaxed),
             total_datagrams_in: self.total_datagrams_in.load(Ordering::Relaxed),
             total_datagrams_out: self.total_datagrams_out.load(Ordering::Relaxed),
+            detected_protocols: vec![],
         }
     }
 }

rust/crates/rustproxy/src/lib.rs

@@ -937,8 +937,31 @@ impl RustProxy {
     }
 
     /// Get current metrics snapshot.
+    /// Includes protocol cache entries from the HTTP proxy service.
     pub fn get_metrics(&self) -> Metrics {
-        self.metrics.snapshot()
+        let mut metrics = self.metrics.snapshot();
+        if let Some(ref lm) = self.listener_manager {
+            let entries = lm.http_proxy().protocol_cache_snapshot();
+            metrics.detected_protocols = entries.into_iter().map(|e| {
+                rustproxy_metrics::ProtocolCacheEntryMetric {
+                    host: e.host,
+                    port: e.port,
+                    domain: e.domain,
+                    protocol: e.protocol,
+                    h3_port: e.h3_port,
+                    age_secs: e.age_secs,
+                    last_accessed_secs: e.last_accessed_secs,
+                    last_probed_secs: e.last_probed_secs,
+                    h2_suppressed: e.h2_suppressed,
+                    h3_suppressed: e.h3_suppressed,
+                    h2_cooldown_remaining_secs: e.h2_cooldown_remaining_secs,
+                    h3_cooldown_remaining_secs: e.h3_cooldown_remaining_secs,
+                    h2_consecutive_failures: e.h2_consecutive_failures,
+                    h3_consecutive_failures: e.h3_consecutive_failures,
+                }
+            }).collect();
+        }
+        metrics
     }
 
     /// Add a listening port at runtime.

ts/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@push.rocks/smartproxy',
-  version: '26.0.0',
+  version: '26.2.1',
   description: 'A powerful proxy package with unified route-based configuration for high traffic management. Features include SSL/TLS support, flexible routing patterns, WebSocket handling, advanced security options, and automatic ACME certificate management.'
 }

ts/proxies/smart-proxy/models/metrics-types.ts

@@ -72,6 +72,7 @@ export interface IMetrics {
     byBackend(): Map<string, IBackendMetrics>;
     protocols(): Map<string, string>;
     topByErrors(limit?: number): Array<{ backend: string; errors: number }>;
+    detectedProtocols(): IProtocolCacheEntry[];
   };
 
   // UDP metrics
@@ -113,6 +114,28 @@ export interface IMetricsConfig {
   prometheusPrefix: string;        // Default: smartproxy_
 }
 
+/**
+ * Protocol cache entry from the Rust proxy's auto-detection cache.
+ * Shows which protocol (h1/h2/h3) is detected for each backend+domain pair,
+ * including failure suppression state with escalating cooldowns.
+ */
+export interface IProtocolCacheEntry {
+  host: string;
+  port: number;
+  domain: string | null;
+  protocol: string;
+  h3Port: number | null;
+  ageSecs: number;
+  lastAccessedSecs: number;
+  lastProbedSecs: number;
+  h2Suppressed: boolean;
+  h3Suppressed: boolean;
+  h2CooldownRemainingSecs: number | null;
+  h3CooldownRemainingSecs: number | null;
+  h2ConsecutiveFailures: number | null;
+  h3ConsecutiveFailures: number | null;
+}
+
 /**
  * Per-backend metrics
  */

ts/proxies/smart-proxy/rust-metrics-adapter.ts

@@ -1,4 +1,4 @@
-import type { IMetrics, IBackendMetrics, IThroughputData, IThroughputHistoryPoint } from './models/metrics-types.js';
+import type { IMetrics, IBackendMetrics, IProtocolCacheEntry, IThroughputData, IThroughputHistoryPoint } from './models/metrics-types.js';
 import type { RustProxyBridge } from './rust-proxy-bridge.js';
 
 /**
@@ -216,6 +216,9 @@ export class RustMetricsAdapter implements IMetrics {
       result.sort((a, b) => b.errors - a.errors);
       return result.slice(0, limit);
     },
+    detectedProtocols: (): IProtocolCacheEntry[] => {
+      return this.cache?.detectedProtocols ?? [];
+    },
   };
 
   public udp = {